Device and method for avoiding hearing damage during activation of vehicle occupant restraint systems

ABSTRACT

A device and a method for preventing damage to hearing which may result from activation of vehicle occupant restraint systems operate using a source of sound for producing a primary sound event having a sound pressure level non-injurious to hearing. The sound pressure level is, however, sufficient to trigger the so-called acoustic reflex of the human ear which has the effect that the ear&#39;s sensitivity is reduced when exposed to high sound pressure levels and the subsequent sound event has only a fraction of the negative effects of the primary sound event on the internal ear. The primary sound event needs only be triggered sufficiently shortly in time before the secondary sound event which occurs on activation of the restraint system and features a sound pressure level injurious to hearing.

The invention relates to a device and a method for preventing damage tohearing which may result from activation of vehicle occupant restraintsystems.

In vehicle occupant restraint systems, for example, gas bag restraintsystems or belt tensioners, gas generators in the form of pyrotechnicgas generators, hybrid gas generators or compressed gas storages areprovided which when activated result in a sound event in the form of aloud bang due to the sudden release of energy. In the case of gas bagrestraint systems the deployment of the gas bag, in addition, isassociated with a strong noise development. The sound pressure levelsinvolved may be so high that damage to hearing of the vehicle occupantsmay result. Since the protective effect of a restraint system depends,among other things, on the short time needed to inflate a gas bag or onfast tensioning of the belt the risk of damage to hearing has hithertohad to be put up with.

Such a damage to hearing may be a blast trauma, also called an auditorytrauma, or an explosion or detonation trauma, one or both of which maybe involved in activation of the restraint system, more particularly, ofa gas bag restraint system. However, it is not always the case thatdamage to hearing is involved on activation of a restraint system,instead damage to hearing is more often something seldom. The occurrenceof damage to hearing depends on a wealth of factors, e.g. on the natureof the gas generator, the gas bag, passenger space volume of thepassenger compartment in the vehicle and on the constitution, moreparticularly, the age of the vehicle occupant concerned. This is whythere are no exact sound level limits for defining damage to hearing.Researching critical sound level limits, as of which damage to hearingoccurs, is very difficult since the sound pressure level greatly dependson the kind of measuring instrument employed. In general, however, itcan be said that the sound pressure level as of which damage to hearingis involved must be all the more higher the shorter the duration of thesound pulse affecting the ear. As a rule a blast trauma occurs in thecase of sound pulses of up to 2 ms duration and peak sound pressurelevels exceeding roughly 150 dB. A blast trauma results in inner earinjury, more particularly to injury of the cochlea due to ahigh-frequency sound event. The symptoms of a blast trauma extend from ashort stabbing ear pain or a so-called tinnitus (persistent whistlingnoise in the upper frequency range) to a so-called tone drop, i.e. aloss of hearing in certain frequency ranges, this last symptom alsobeing termed threshold shift which may be of a temporary nature(TTS-Temporary Threshold Shift) or permanent (PTS-Permanent ThresholdShift).

Unlike a blast trauma an explosion trauma is caused by a sound eventhaving a peak sound pressure level lasting more than 2 ms and in thecase of a sound pressure level of more than approx. 150 dB. An explosiontrauma is frequently associated with a tear in the ear drum andoccasionally with a luxation of the tympanic bone, whereby a loss ofhearing over the complete frequency range may be involved. Accordingly,an explosion trauma is an injury of the inner ear and the middle ear. Anexplosion trauma is caused by sound waves at a low frequency.

On activation of a gas bag restraint system a sound event lastingapprox. 50 ms is caused, the sound event not being in a narrow frequencyrange, it instead taking up a sound spectrum. The sound pressure levelsoccurring as a maximum extend from approx. 120 to 165 dB. The soundevent on activation of a gas bag restraint system begins directly onopening of the compressed gas storage, as a rule on initiation of apyrotechnic ignition charge. The high-speed emission of the gas from thegas generator as well as the deployment of the gas bag itself producesound waves having a high sound pressure level, the peak sound pressurelevels occurring mostly on commencement of the sound event. Thefrequencies of below 300 Hz are, according to the current state ofresearch, responsible for ear drum injury and the frequencies above 300Hz for inner ear injury.

The invention defines a device and a method for preventing damage tohearing, more particularly inner ear injuries, caused by activation ofvehicle occupant restraint systems.

The device in accordance with the invention comprises a source of soundfor producing a primary sound event having a sound pressure levelnon-injurious to hearing, which, however, is sufficient to trigger anacoustic reflex of the human ear, and a activation control for thesource of sound. The activation control triggers the source of sound ina restraint action so that it produces the primary sound event in timeshortly before the occurrence of a secondary sound event which occurs onactivation of the restraint system and features a sound pressure levelinjurious to hearing. The time interval between the sound events, on theone hand, and the sound level of the primary sound event, on the other,are dimensioned so that a damage to hearing as a result of the secondarysound event is prevented.

The method in accordance with the invention provides for production of aprimary sound event having a sound pressure level non-injurious tohearing, which, however, is sufficient to trigger an acoustic reflex ofthe human ear. Also, the primary sound event is produced so shortlybefore the occurrence of the secondary sound event which occurs onactivation of the restraint system and features a sound pressure levelinjurious to hearing that the acoustic reflex is triggered and damage tohearing as a result of the secondary sound event is thereby prevented.

The device and the method in accordance with the invention make use ofthe acoustic reflex of the human ear forming a protective reflex whichinstantly reduces its sensitivity when exposed to high sound pressurelevels so that subsequent sound events having the same or higher soundpressure level have only a fraction of the negative effects of theprimary sound event on the internal ear. As a result of this thesecondary sound event has a lesser physiological effect so that nodamage to the inner ear materializes, such as, for example, blasttrauma.

The acoustic reflex (stapedius reflex) results from contraction of amuscle in the region of the inner ear, as a result of which the tympanicbone stiffens and the sound pressure level is reduced by approx. 5 dB.The stapedius reflex is caused as of a sound pressure level of approx.70 dB, the irritation threshold for triggering the reflex in the case ofa continuous noise being higher. Adapted to the noise level usuallypredominant in a vehicle the source of sound is able to produce aprimary sound event with a sound pressure level in the range of approx.70 to approx. 140 dB to trigger the acoustic reflex.

Due to the device in accordance with the invention it is possible, forexample, to incorporate gas generators nearer to the head of theoccupant in the vehicle.

Preferably, however, the sound pressure level of the primary sound eventshould amount to at least approx. 100 dB, preferably more than approx.110 dB. Since the so-called latency time of the acoustic reflex, i.e.the time between the sound event triggering the reflex up to the changein impedance due to the reflex, becomes less with a primary sound eventhaving a higher sound pressure level, sound events which are relativelyjust below the limit for damage to hearing are best suitable intriggering the acoustic reflex within the shortest time.

The primary sound event triggering the acoustic reflex commences as ofapprox. 0.5 up to approx. 30 ms prior to the secondary sound event. Theoptimum spacing between commencement of the primary sound event and thatof the secondary sound event depends on the sound pressure level of theprimary sound event as a result of the aforementioned interactionbetween the altitude of the sound pressure level and the latency time ofthe acoustic reflex. The latency time of the acoustic reflex extendsfrom approx. 0.5 to more than 150 ms, a time of roughly 30 ms being,however, available at the most, prior to activation of the restraintsystem, depending on the vehicle concerned, for prompting the primarysound event. This is the reason why preferably the primary sound eventcommences approx. 5 to approx. 15 ms prior to the secondary sound event.It always needs to be assured that the sound pressure level and the timeinterval between commencement of the primary sound event andcommencement of the secondary sound event are adapted to each other sothat the latency time of an occupant having a normal hearing function isshorter than the time interval between the commencement of the two soundevents.

The primary sound event is required to have a frequency spectrum in therange of approx. 500 to approx. 8000 Hz, preferably in the range ofapprox. 2000 to approx. 4000 Hz. It is in the latter range that thehuman ear is most sensitive, i.e. a sound wave having a relatively lowsound pressure level is already sensed. In the preferred embodiment thesource of sound produces a sound event having a frequency of approx.3500 Hz. When the primary sound event is produced by the abrupt releaseof energy of an energy storage, for example, a pyrotechnic material,sound waves of a complete spectrum are generated so that the frequencyrange in which the generated sound waves are intended to lie exclusivelycannot be limited, whereas when the sound waves are produced by aloudspeaker the sound events can be generated in narrow frequency rangesor at an exact frequency.

The primary sound event lasts preferably approx. 2 ms at the most. Sinceit exhibits a sound pressure level which is relatively just below thelimit for damage to hearing, hearing injuries due to the primary soundevent need to be excluded. By providing a relatively short primary soundevent the occurrence of an explosion trauma as described above can beexcluded with relatively high probability, this explosion traumaoccurring more particularly in the case of sound events having aduration of more than 2 ms.

The primary sound event may be a short, once-only event in the form of anoise acoustically detectable by the human ear or it may be the resultof several single noises in sequence, of which the primary noisecommences prior to the secondary sound event.

In accordance with one embodiment the source of sound comprises anenergy storage which is for example a compressed gas storage or containspyrotechnic material. The abrupt release of the energy results in theprimary sound event.

Alternatively, the source of sound may also feature a loudspeaker, forinstance a piezoelectric loudspeaker by means of which sound eventslasting relatively longer may be produced.

The activation control includes preferably a crash sensor, in responseto the signal of which in restraint action the primary sound event isproduced, as well as in the case of the preferred embodiment a controlunit connected to the crash sensor. In this arrangement the control unitis configured so that it, with a predetermined delay after havingreceived a signal from the crash sensor, outputs a signal to the sourceof sound for triggering the primary sound event. The crash sensor may bea delay sensor for sensing vehicle deceleration, or a tactile sensor asis used for instance to activate side gas bags and which sensesdeformation of the vehicle in a crash situation. In addition, the crashsensor and the control unit may be configured so that they can sense acrash which can no longer be avoided, by, for example, a spacing sensorbeing provided which is able to sense the distance away of objectsrelative to the vehicle. The control unit then computes, for example, onthe basis of the actual vehicle speed whether the object approachingrelative to the vehicle can still be avoided. In this way it is possibleto set the point in time for activating the primary sound event evenprior to commencement of a collision. This may prove necessary in thecase of a compact car for instance in which the time delay between firstdeformation of the vehicle and activation of the restraint system aswell as the associated production of the secondary sound event is sosmall that even in the case of instant activation of the primary soundevent at commencement of a vehicle contact in the case of a head-oncollision not enough time is available for the human ear to trigger theacoustic reflex completely.

The device in accordance with the invention may be configured as aseparate assembly and, where appropriate, retrofitted in existingvehicles with restraint systems. The device comprises a completeactivation control of its own, a common delay sensor or even a controlunit in common with the vehicle occupant restraint system. When a commoncontrol unit is incorporated, control of the timing sequence of theprimary sound event and secondary sound event is even simpler and moreprecise.

Since the space requirement for the device in accordance with theinvention is slight, it is also possible to integrate it in a restraintsystem.

The invention defines further a gas bag restraint system for vehicleoccupants including a gas bag, a gas generator and an activation controlcomprising a delay sensor and a control unit. The device in accordancewith the invention as described above for preventing damage to hearingas may result from activation of the vehicle occupant restraint systemis in this arrangement integrated in the gas bag restraint system.

In addition, a common activation control for activating the gasgenerator and triggering the primary sound event is preferably provided.

The gas bag restraint system may be configured modular, the gas bagmodule then being incorporated as a preassembled unit in a vehicle. Inthis case the source of sound of the device for preventing damage tohearing comprises an energy storage, the energy of which is abruptlyreleased to provide the primary sound event. At least this energystorage forms together with the module, in which it is integrated, acomplete preassembled unit.

In accordance with a further embodiment at least the energy storage ofthe device is integrated in the gas generator of the gas bag restraintsystem.

Further features and advantages of the invention will be appreciatedfrom the following description of several preferred embodiments and fromthe following drawings to which reference is made and in which:

FIG. 1 is a simplified representation of a first embodiment of thedevice in accordance with the invention in which the device isconfigured as an assembly separate from the vehicle occupant restraintsystem and operates in accordance with the method according to theinvention;

FIGS. 2a to 2 d show various embodiments of the source of sound providedin the device in accordance with the invention;

FIGS. 3a to 3 c show various embodiments of the crash sensors providedin the device in accordance with the invention;

FIG. 4 shows a second embodiment of the device in accordance with theinvention in which it is coupled to a vehicle occupant restraint systemin the form of a gas bag restraint system or a belt tensioner system;

FIG. 5 shows a third embodiment of the device in accordance with theinvention in which it is likewise coupled to a gas bag restraint systemin accordance with the invention;

FIG. 6 shows a fourth embodiment of the device in accordance with theinvention in which it is integrated in a gas bag module;

FIG. 7 shows the gas bag restraint system in accordance with theinvention in which the source of sound of the device in accordance withthe invention is integrated in the gas generator of the gas bagrestraint system; and

FIG. 8 shows a further embodiment of the gas bag restraint system inaccordance with the invention.

In FIG. 1 a device 10 for preventing damage to hearing is representedgreatly simplified which may be caused by activation of a vehicleoccupant restraint system (not shown), for example, a gas bag restraintsystem or a belt tensioner system. The device 10 comprises a source ofsound 12 and an activation control 14 for the source of sound 12. Theactivation control 14 in turn features a crash sensor 16 and, connectedthereto, a control unit 18 to which the source of sound 12 is connected.

The source of sound 12 can be configured differingly as evident from theFIGS. 2a to 2 d. It is possible to configure the source of sound 12 as ausual loudspeaker 20 (cf. FIG. 2a) or as a piezoelectric loudspeaker 22(cf. FIG. 2b). In addition, a sound event to be produced by the sourceof sound may also be prompted by ignition of pyrotechnic material 24accommodated in a housing 26 (cf. FIG. 2c). In this arrangement anigniter 28 connected to the control unit 18 protrudes into the housing26. In the embodiment shown in FIG. 2c the source of sound 12 isconfigured like a low-power gas generator for vehicle occupant restraintsystems. In accordance with FIG. 2d the source of sound 12 is configuredas a compressed gas storage 30 having a chamber 32 filled withcompressed gas. In a restraint action an opening in a wall 34 of thecompressed gas storage is made clear through which the compressed gasemerges, thereby producing a sound event. The sound event may also beproduced by, for example, detonation gas contained in the chamber 32being ignited, which due to the high pressure within the chamber breaksopen the wall 34 at predetermined positions, allowing the gas to streamoutwardly under high pressure and thereby producing a sound event. As inthe case of the embodiment shown in FIG. 2c also the compressed gasstorage 30 according to FIG. 2d is configured the same as a gasgenerator used hitherto as usual in vehicle occupant restraint systems,its capacity merely being very much less. While the sources of sound inaccordance with FIGS. 2a and 2 b are capable of producing a sound eventlonger in duration or several sound events in sequence, the sources ofsound shown in FIGS. 2c and 2 d are merely able to activate a shortsound event since they consist of an energy storage the energy of whichis released abruptly, thereby generating sound waves.

In the FIGS. 3a to 3 c various embodiments of the crash sensor providedin the case of the device in accordance with the invention are depicted.Accordingly, the sensor may be a delay sensor 16 a (FIG. 3a), a tactilesensor 16 b (FIG. 3b) or a spacing sensor 16 c (FIG. 3c). In the case ofthe delay sensor 16 a, for instance, a rotatively mounted part, which ina restraint action swivels from-its basic position, closes an electricalcircuit. In the case of the tactile sensor 16 b two plates slightlyspaced from each other are provided which for instance are provided inmounting the bumpers and which come into contact with each other whenslightly deformed so that an electrical circuit is closed. The spacingsensor 16 c according to FIG. 3c transmits at regular intervals pulseswhich are reflected from an object, for example, an object approachingrelative to the vehicle, and are re-sensed by the sensor. Thecorresponding signals are evaluated by the control unit 18 to determinethe spacing and the speed of the object moving relatively towards thevehicle and to draw conclusions therefrom as to whether a collision isimminent. For this reason the spacing sensor 16 c communicatescontinuously with the control unit 18.

The device 10 shown in FIG. 1 is incorporated in a vehicle fitted outwith a vehicle occupant restraint system. Irrespective of whether thevehicle occupant restraint system works with a pyrotechnic gasgenerator, a hybrid gas generator or a compressed gas storage, onactivation of the vehicle occupant restraint system a loud bang occurs,the sound pressure level of which may result in damage to hearing of thevehicle occupants in the region of the internal ear, among otherregions. The device 10 shown in FIG. 1 prevents such damage to hearingby making use of the acoustic reflex of the ear, this namely loweringits sensitivity following the action of a sound event having a highsound pressure level so that a subsequent sound event has lesserphysiological effects on the ear, more particularly on the inner ear,even if the secondary sound event were to have a higher sound pressurelevel than the primary sound event.

When the delay sensor 16 a as shown in FIG. 3a is used, in a restraintaction, as of a predetermined vehicle deceleration value being attained,this delay sensor which may be configured as a mechanical,electromechanical or electrical delay sensor, generates a signal whichis passed on to the control unit 18. The latter processes the signal andactuates the source of sound 12 with a predetermined time delay.Depending on how the source of sound 12 is configured, a primary soundevent of a more or less long duration is produced, the sound pressurelevel of which is sufficiently high to trigger the acoustic reflex,without being so high, however, that it could result in damage tohearing. The primary sound event lasts less than 2 ms, attains a soundpressure level of at least approx. 100 dB and lies preferably in therange of 110 to 140 dB. When a loudspeaker 20, 22 is used as the sourceof sound 12 the frequency of the primary sound event can bepredetermined in tight limits. In this case the frequency spectrum ofthe primary sound event is preferably in the range of approx. 2000 toapprox. 4000 Hz, the ear being particularly sensitive to triggering theacoustic reflex at sound events at about 3500 Hz. When using an energystorage, as is depicted in FIGS. 2c and 2 d, a sound event is producedwhich covers a complete sound spectrum. The control unit 18 controls thesource of sound 12 at such an early time that the primary sound eventoccurs shortly before the secondary sound event which is triggered onignition of the gas generator provided. The minimum offset in timebetween commencement of the primary sound event and that of thesecondary sound event should be in the range of approx. 5 to 15 ms, i.e.sufficiently large to activate the protective effect by the acousticreflex in the human ear.

The device 10 shown in FIG. 1 is configured as a separate assembly whichmay also be retrofitted in a vehicle equipped with a restraint system.The timing sequence of the primary sound event and secondary sound eventcan, however, be better controlled when the device is integrated in avehicle occupant restraint system or forms a part thereof, asrepresented in FIGS. 4 to 8.

In the embodiment as shown in FIG. 4 the device 10 is coupled to a gasbag restraint system 36 which comprises a folded gas bag 38 and an gasgenerator 40 arranged in the interior thereof. Activation of the gasgenerator 40 is done via an activation control 42 which is formed by acontrol unit 44 and a delay sensor 46. The activation control 42represents a control common to the device 10 and the gas bag restraintsystem 36. In a crash situation the control unit 44, on receiving acorresponding signal from the delay sensor 46, first outputs a signal tothe source of sound 12 and, in a brief time delay thereafter, asecondary signal to the gas generator 40 so that the source of sound 12produces a primary sound event shortly before ignition of the gasgenerator 40 and the secondary sound event involved therein.

Instead of being coupled to the activation control 42 of a gas bagrestraint system 36, the device 10 may also be employed for preventingdamage to hearing which may occur on activation of a belt tensioningsystem 48, as is likewise depicted in FIG. 4. Although damage to hearingdue to activation of a belt tensioning system has yet to be reported,this may be due to the fact that hitherto gas generators have not beenarranged in the vicinity of the head of the occupant. Belt tensioningsystems are conceivable, however, in which it would be an advantage toarrange the gas generator in the vicinity of the head. In this case thesound pressure level could be high enough to result in damage tohearing, also in the inner ear region, so that it is of advantage toprovide the device 10. The belt tensioning system 48 comprises, amongother things, a piston/cylinder unit 50, the piston being connected to abelt buckle 52. Pyrotechnic propellant material 54 is ignited by theactivation control 42 slightly delayed in time after the primary soundevent so that also the high sound pressure level on activation of thebelt tensioning system 48 cannot lead to damage to hearing.

The arrangement shown in FIG. 4 may, however, also be modified so thatthe activation control 42 is coupled to both the belt tensioning system48 and to the gas bag restraint system 36. Since the belt tensioningsystem 48 is usually activated in time prior to the gas bag restraintsystem 36 the gas generator of the belt tensioning system 48 may beemployed as the source of sound by the pyrotechnic propellant material54 being ignited in time sufficiently prior to activation of the gasgenerator 40 of the gas bag restraint system 36. In this case theseparate source of sound 12 can be eliminated.

The embodiment shown in FIG. 5 differs from that shown in FIG. 4 merelyby the device 10 and the gas bag restraint system 36 being coupled toeach other by a common delay sensor 56. Instead of a common control unit44, however, two separate control units 58 and 60 may be provided forthe device 10 and the gas bag restraint system 36 respectively.

Since the device 10 is configured very small it can be integrated in agas bag module as is evident from FIG. 6. A gas bag module comprises,for instance, a preassembled unit consisting of the gas generator 40 andthe gas bag 38, as is evident from FIG. 6. For this purpose the sourceof sound 12 is secured to a base plate 62 as part of the module to whichalso the gas generator 40 and the gas bag 38 can be attached and whichserves for securing the gas bag module with the source of sound 12 to asteering wheel hub (not shown). Between the source of sound 12 and anigniter 72 protruding into the interior of the gas generator 40 anignition delay element 63 is arranged. The signal for generating theprimary sound event which is directed to the source of sound 12, isrouted from the latter to the ignition delay element 63 and from thereto the igniter 72 so that the commencement of the primary sound eventhas a predetermined time interval with regard to the commencement of thesecondary sound event. The ignition delay element 63 may be configuredas a capacitor, for instance. The arrangement shown in FIG. 6 is verysimple in configuration, particularly as regards its circuitry.

In this embodiment too, the primary sound event is produced by ignitionof a pyrotechnic material so that the source of sound 12 is configuredas a gas generator. The gas generated on ignition of the pyrotechnicmaterial contained in the source of sound 12 can be used to prepareactivation of the gas bag restraint system. For this purpose the gasgenerated is introduced into a positioning means 82, for example, in theform of folded tubing. This tubing is arranged in the vehicle so thatit, in its inflated condition, opens a gas bag cover, as a result ofwhich deployment of the gas bag 38 can occur quicker. Furthermore, thetubing 82 may be configured as a tensioning tape which positions thefolded gas bag 38, it thereby also permitting speedier deployment of thegas bag 38. Positioning the gas bag 38 is of advantage especially in thecase of it being configured as a side gas bag needing to be deployedextremely fast, for example, in the case of a head-side gas bagextending from the A pillar to the C pillar. If a central gas supplysystem (not shown) is provided in the vehicle the positioning means 82may also prepare supply of the gas to the gas bag 38 or actuate acorresponding switching device to release the gas. In this case theigniter 72 as well as the ignition delay element 63 would be eliminated,instead of which a gas line would lead directly into the interior of thegas bag 38.

In the case of the embodiment depicted in FIG. 7 the source of sound 12is even integrated in the gas generator 61 of a gas bag restraint system36. The interior of a housing 64 accommodates two chambers, the firstchamber 66 being filled with pyrotechnic material which on being ignitedproduces gas for the deployment of a gas bag 38. The second,substantially smaller chamber 68 also filled with pyrotechnic materialserves as the source of sound 12. Two separate igniters 70, 72 for thechambers 66, 68 are activated one after the other in time by the controlunit 44 so that first the pyrotechnic material in chamber 68 is ignited,gas emerging from the chamber and providing the primary sound event.Subsequently the pyrotechnic material of the first chamber 66 is ignitedto cause the gas bag 38 to be deployed by the gas generated thereby.

The embodiment of a gas bag restraint system 36 shown in FIG. 8corresponds substantially to that shown in FIG. 7, except that the gasgenerator 40 is configured as a compressed gas storage or hybridstorage. The pyrotechnic material surrounding the igniter 72 thus servesto open the gas generator housing. However, the igniters 70, 72 areconnected to each other via an ignition delay element 63 arranged in theinterior of the gas generator so that the control unit 44 does not needto control the two igniters 70, 72 separate from each other. Since thechamber 68 protrudes into the interior of the gas generator housing inwhich gas is stored under pressure, the heat produced on ignition of thepyrotechnic material accommodated in the chamber 68 is supplied to thegas via a wall defining the chamber 68. The intention behind thisarrangement is that the power developed by a compressed gas storage orhybrid storage needs to be constant over the temperature range of from−35° C. to approx. 85° C. Since at extremely low temperatures, moreparticularly at temperatures below the freezing point, the power of thegas generator is reduced, the gas can be heated up by the ignition ofthe pyrotechnic material accommodated in the chamber 68. To prevent gaswhich is already hot from being heated up even further, the control unit44 may be connected to a temperature sensor which senses the temperatureof the gas in the interior of the gas generator 61. If the temperatureof the gas is below a predetermined critical temperature, for example,0° C., the igniter 70 is activated in the restraint action. Should,however, preheating the gas no longer be necessary because thetemperature of the gas exceeds the critical temperature, a second sourceof sound 84 located outside of the gas generator 61 is activated.

The device 10 and the gas bag restraint systems shown in the variousFigures are suitable not only for being incorporated in a steering wheelor in the dashboard. Since especially in the case of head gas bagrestraint systems and side gas bag restraint systems the gas generatorsneed to deploy the gas bags extremely fast, sound events having a higherfrequency and higher sound pressure levels are produced on gas beingemitted from the gas generator than is the case with a gas generatoraccommodated in the steering wheel or in the dashboard.

What is claimed is:
 1. A device for preventing damage to hearing whichmay result from activation of a vehicle occupant restraint system, saiddevice comprising: a source of sound (12) for producing a primary soundevent having a sound pressure level non-injurious to hearing and fortriggering an acoustic reflex of the human ear, and an activationcontrol (14, 42) for said source of sound (12), said activation control(14, 42) triggering said source of sound (12) to produce said primarysound event and providing a time delay before the occurrence of asecondary sound event having a sound pressure level injurious to hearingoccurring on activation of the restraint system, said time delay betweenthe secondary sound event and said primary sound event allowing saidacoustic reflex to occur so that damage to hearing as a result of saidsecondary sound event is prevented.
 2. The device according to claim 1wherein said source of sound (12) produces a primary sound event havinga sound pressure level in the range of approximately 70 to approximately140 dB.
 3. The device according to claim 1 wherein said source of sound(12) produces a primary sound event having a sound pressure level of atleast approximately 100 dB.
 4. The device according to claim 1 whereinsaid primary sound event commences approximately 0.5 to approximately 30ms prior to said secondary sound event.
 5. The device according to claim1 wherein said primary sound event commences approximately 5 toapproximately 15 ms prior to said secondary sound event.
 6. The deviceaccording to claim 1 wherein said source of sound (12) produces a soundevent having a frequency spectrum in the range of approximately 500 toapproximately 8000 Hz.
 7. The device according to claim 1 wherein saidsource of sound (12) produces a sound event having a frequency spectrumin the range of approximately 2000 to approximately 4000 Hz.
 8. Thedevice according to claim 1 wherein said source of sound (12) produces asound event having a frequency of approximately 3500 Hz.
 9. The deviceaccording to claim 1 wherein said primary sound event does not exceedapproximately 2 ms.
 10. The device according to claim 1 wherein saidsource of sound (12) includes an amount of stored energy which, whenabruptly released, produces said primary sound event.
 11. The deviceaccording to claim 10 wherein said amount of stored energy ispyrotechnic material (24) which, when ignited, produces said primarysound event.
 12. The device according to claim 10 wherein said amount ofstored energy is a compressed gas.
 13. The device according to claim 1wherein said source of sound (12) is a loudspeaker (20, 22).
 14. Thedevice according to claim 13 wherein said loudspeaker is a piezoelectricloudspeaker (22).
 15. The device according to claim 1 wherein saidactivation control (14, 42) includes a crash sensor (16, 16 a, 16 b, 16c, 46, 56), for producing a signal for triggering said primary soundevent in response to sensing a vehicle crash.
 16. The device accordingto claim 15 wherein said activation control (14, 42) and said crashsensor (16 c) sense an impending vehicle crash.
 17. The device accordingto claim 16 wherein said crash sensor (16 c) is a spacing sensor forsensing the distance of an object from the vehicle.
 18. The deviceaccording to claim 15 wherein said crash sensor (16 b) is a tactilesensor which generates a signal in response to sensing a deformation ofthe vehicle.
 19. The device according to claim 15 wherein said crashsensor (16 a, 46, 56) is a delay sensor for sensing the vehicledeceleration.
 20. The device according to claim 15 wherein saidactivation control (14, 42) includes a control unit (18, 44, 58)connected to said crash sensor (16, 46, 56), said control unit producesan output signal to said source of sound to produce said primary soundevent in response to a signal from said crash sensor (16, 46, 56)indicating the occurrence of a vehicle crash.
 21. The device accordingto claim 15 wherein said device is coupled to said vehicle occupantrestraint system, and wherein said crash sensor (46, 56) is sharedbetween said device (10) and said vehicle occupant restraint system. 22.The device according to claim 20 further comprising a control unit (44)connected to said crash sensor (46) for controlling the time delaybetween said primary sound event and said secondary sound event.
 23. Agas bag restraint system for vehicle occupants comprising: a gas bag(38), a gas generator (40, 61), an activation control (42) having acrash sensor (46) and a control unit (44), and a device (10) integratedinto said gas bag restraint system (36) for preventing damage to hearinghaving a source of sound (12) for producing a primary sound event havinga sound pressure level non-injurious to hearing and for triggering anacoustic reflex of the human ear.
 24. The gas bag restraint systemaccording to claim 23 wherein said activation control (42) activatesboth said gas generator (40, 61) and said primary sound event.
 25. Thegas bag restraint system according to claim 24 wherein said gasgenerator (40, 61) includes an igniter (72) and an ignition delayelement (63) mounted between said igniter (72) and said source of sound(12), said ignition delay element delays the signal from said activationcontrol to said igniter (72) by a predetermined time delay.
 26. The gasbag restraint system according to claim 23 further including a gas bagmodule, and wherein said source of sound (12) includes an amount ofstored energy integrated into said gas bag module which, when abruptlyreleased, produces said primary sound event.
 27. The gas bag restrainsystem according to claim 26 wherein said amount of stored energy isintegrated into said gas generator (61).
 28. The gas bag restraintsystem according to claim 23 wherein a first source of sound (68)contains pyrotechnic material which, when ignited, produces said primarysound event and releases heat energy which is directed into said gasgenerator (61).
 29. The gas bag restraint system according to claim 28wherein said first source of sound (68) is only activated when thetemperature of said gas generator (61) is below a predetermined criticaltemperature, and wherein a second source of sound (84) is provided whichis only activated to produce said primary sound event when said criticaltemperature is exceeded.
 30. The gas bag restraint system according toclaim 23 wherein said primary sound event is produced by ignition of apyrotechnic material, said ignition generating an amount of gas which isthereby introduced into a positioning means (82) for preparing a morespeedy deployment of the gas bag (38).
 31. The gas bag restraint systemaccording to claim 23 wherein said primary sound event is produced byignition of a gas generator which is a part of a belt tensioning system(48).
 32. A method for preventing damage to hearing which may resultfrom activation of a vehicle occupant restraint system, said methodincluding the steps of: providing a primary sound event having a soundpressure level non-injurious to hearing and sufficient to trigger anacoustic reflex of the human ear, providing a time delay to allow saidacoustic reflex to occur, activating said vehicle occupant restraintsystem which produces a secondary sound event having a sound pressurelevel injurious to hearing, said time delay between the secondary soundevent and said primary sound event allowing said acoustic reflex tooccur so that damage to hearing as a result of said secondary soundevent is prevented.
 33. The method according to claim 32 wherein saidprimary sound event has a sound pressure level in the range ofapproximately 70 to approximately 140 dB.
 34. The method according toclaim 32 wherein said primary sound event has a sound pressure level ofat least approximately 100 dB.
 35. The method according to claim 32wherein said primary sound event commences approximately 0.5 toapproximately 30 ms prior to said secondary sound event.
 36. The methodaccording to claim 32 wherein said primary sound event commencesapproximately 5 to approximately 15 ms prior to said secondary soundevent.
 37. The method according to claim 32 wherein said primary soundevent has a frequency spectrum of approximately 500 to approximately8000 Hz.
 38. The method according to claim 32 wherein said primary soundevent has a frequency spectrum of approximately 2000 to approximately4000 Hz.
 39. The method according to claim 32 wherein said primary soundevent has a frequency of approximately 3500 Hz.
 40. The method accordingto claim 32 wherein said primary sound event does not exceedapproximately 2 ms.